【ccf- csp201509-4】高速公路

#include<iostream>
using namespace std;
void DFS(int**mat, int *mark,int *sp, int n, int p)
{
    int i;
    //DFS每个顶点
    if(!mark[p])
    for(i=1;i<=n;i++)
        if (mat[p][i]&&i!=p)//<p,i>
        {
            mark[p] = 1;
            sp[p] = 1;
            DFS(mat,mark,sp, n, i);
            mark[p] = 0;
        }
}
int main()
{
    int n, m,i,j; cin >> n >> m;
    int**mat = new int*[n+1];
    for (i = 0; i <= n; i++)
        mat[i] = new int[n+1];
    for (i = 0; i <= n; i++)
        for (j = 0; j <= n; j++)
            mat[i][j] = 0;
    int a, b;
    for (i = 0; i < m; i++)
    {
        cin >> a >> b;
        mat[a][b] = 1;
    }
    int *mark = new int[n + 1];
    int *sp = new int[n + 1];
    int sum = 0,k;
    for (i = 1; i <= n; i++)
        mark[i] = 0;
    for (i = 1; i < n; i++)
    {
        for (k = 1; k <= n; k++)
            sp[k] = 0;
        DFS(mat, mark, sp, n, i);
        for (j = i + 1; j <= n; j++)
        {
            if (sp[j])//<i,j>
            {
                for (k = 1; k <= n; k++)
                    sp[k] = 0;
                DFS(mat, mark, sp, n, j);
                if (sp[i])//<j,i>
                    sum++;
            }
        }
    }
    cout << sum << endl;
    return 0;
}